Determining course from coordinate to coordinate

Question

I have two points (latitude1, longitude1) and (latitude2, longitude2). How do I determine in PHP the course needed to be taken from point 1 to point 2?

Course would be North, South, East, or West which would probably be converted from degrees?

Thanks!

Answer 1

// Function: latlon_bearing_great_circle
// Desc:  This function calculates the initial bearing you need to travel
//   from Point A to Point B, along a great arc.  Repeated calls to this
//   could calculate the bearing at each step of the way.
function latlon_bearing_great_circle($lat_a, $lon_a, $lat_b, $lon_b) {
// Convert our degrees to radians:
list($lat1, $lon1, $lat2, $lon2) =
    _deg2rad_multi($lat_a, $lon_a, $lat_b, $lon_b);

// Run the formula and store the answer (in radians)
$rads = atan2(
        sin($lon2 - $lon1) * cos($lat2),
        (cos($lat1) * sin($lat2)) -
              (sin($lat1) * cos($lat2) * cos($lon2 - $lon1)) );

// Convert this back to degrees to use with a compass
$degrees = rad2deg($rads);

// If negative subtract it from 360 to get the bearing we are used to.
$degrees = ($degrees < 0) ? 360 + $degrees : $degrees;

return $degrees;
}

// Function: _deg2rad_multi
// Desc: A quick helper function.  Many of these functions have to convert
//   a value from degrees to radians in order to perform math on them.
function _deg2rad_multi() {
    // Grab all the arguments as an array & apply deg2rad to each element
    $arguments = func_get_args();
    return array_map('deg2rad', $arguments);
}

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